Diamond has a wide band gap, the highest thermal conductivity among materials, and a high chemical stability. Therefore, applications of diamond to semiconductor devices have been studied. A semiconductor device using diamond stably operates in a high temperature environment and in a space environment and can withstand a high-speed, high-power operation. Therefore, a demand thereof is high. In addition, high-performance electronic devices such as deep UV-emitting devices and electron emission sources utilizing unique features of diamond, which cannot be constructed by using other materials, can be manufactured.
In order to use the diamond as a material for a semiconductor device, it is necessary to control p-type or n-type electric conduction. A p-type diamond semiconductor exists in nature, and it is relatively easy to artificially synthesize the p-type diamond semiconductor. For example, if a compound containing boron is introduced as a source of impurities into a chamber when performing chemical vapor deposition (CVD) with diamond, the p-type diamond semiconductor can be obtained.
On the other hand, an n-type diamond semiconductor does not exist in nature, and until now, it has been believed that it is impossible to artificially synthesize the n-type diamond semiconductor. In 1997, the n-type diamond semiconductor was obtained by epitaxially growing diamond while doping a {111}-facet diamond single crystal substrate with phosphorus as an n-type impurity (refer to Patent Literature 1). However, at that time, when the diamond is epitaxially grown while doping a {100}-facet diamond single crystal substrate with n-type impurities in such synthesis conditions as disclosed in Patent Document 1, there are problems in that doping efficiency is very low, the n-type impurities are not almost accepted, and a conductive property is not nearly obtained.
The {111}-facet diamond single crystal substrate has problems in that it can not be obtained in a large area with high quality by a high-temperature and high-pressure method, and by a chemical vapor deposition method, and it is difficult to lower the cost. On the other hand, the {100}-facet diamond single crystal substrate is relatively easily realized in a large area with high quality. Therefore, in developing electronic devices, a technique of growing the n-type diamond semiconductor on the {100} facet has become essential.
In recent years, two techniques of growing an n-type diamond semiconductor on the {100}-facet diamond single crystal substrate have been proposed.
(1) A method of growing an n-type diamond semiconductor on the {111} facet, which is formed on the {100} facet, by processing the {100} facet and growing the {111} facet on the {100} facet under control of a parameter upon the diamond growing (refer to Patent Literature 2).
(2) A method of epitaxially growing diamond while directly doping the {100}-facet diamond single crystal substrate with n-type impurities under in synthesis conditions different from those of Patent Document 1 (refer to Patent Literature 3).
In these methods, basically, p-type and n-type diamond semiconductors can be grown without limitation of the facet orientation of the substrate. Currently, research and development of pn junction type and pin junction type semiconductor devices have been made based on the aforementioned techniques.
In general semiconductor synthesizing technology, a technique of burying semiconductors in specific positions and a technique of selectively growing semiconductors are very important. The other semiconductor materials representatively including silicon can be used to synthesize p-type and n-type semiconductors with use of an ion implantation method, and a selectively buried semiconductor area can be formed by an ion implantation method. On the other hand, with respect to the diamond semiconductor, for the reason that defects occurring from the ion implantation cannot be easily recovered by thermal treatment and the implanted impurities are not accepted at substitution positions, it is believed that it is substantially impossible to produce the above-mentioned buried semiconductor area.    [Patent Literature 1] JP-A-10-81587 (“JP-A” means unexamined published Japanese patent application)    [Patent Literature 2] WO 2003/106743    [Patent Literature 3] JP-A-2006-240983